Condenser reproducer



May 20, 1930. P. E. EDELMAN 1,759,810

CONDENSER REPRODUCER Filed April 11, 1929 4 Sheets-Sheetl May 20, 1930.

P. E. EDELMAN CONDENSER REPRODUCER 4 Sheets-Sheet 2 Filed April 11, 1929 May 20, 1930. P. E. EDELMAN CONDENSER REPRODUCER Filed April 1l, 3.929 4 Sheets-Sheet 5 May 20, 1930. P. E. EDELMAN 1,759,810

CONDENSER REPRODUCER Filed April 11, 1929 4 Sheets-SheetI 4 Patented `May 20, 1930 vUNITED STATES PATENT OFFICE PHILIP E. EDELMAN, OF CHICAGO, ILLINOIS, .ASSIGNOB 10 EPHRAIM BANNING, 0F CHICAGO, ILLINOIS CONDENSER REPRODUCER Application med April 11,

My present invention relates to improvements in a condenser reproducer. An object of this invention is to provide greater tonal response and fidelity of overtones in reproduction than'has heretofore been possible.

A further object is to provide a simple inexpensive structure and combination of the parts for uniform production.

These and various other ollxjet, las

resentl a ear, arevaccomp is e y is lo ipnventioii wlhlich is fully described in they following specification, and shown in the accompanying drawings, in which- Figure 1 is a rear elevation of a condenser frame; p

Fig. 2 is a front elevation of a suitablel construction for the flexible electrode of the condenser reproducer;

Fig. 3 is a section of a crinkled tinsel metalline cloth used in the structure of Fig. 2;

Fig. 4 is a section of a part of the dielectrlc diaphragm and its metal coating;

Fig. 5 is a diagram sectioned to show the dissimilar areas working in the two flexlble electrodes;

Fig. 6 is a part section view showing the relative assembly of the diaphragm parts;

f Fig. 7 is a part section showing how the varnish size used fills in defects in the diaphragm fabric;

Fig. 8 is a plan view; Fig. 9 is a sectional view of a portion of a modified construction for the permeable elecf trode; and v Fig. 10 is a diagram of a suitable operating circuit for the condenser reproducer.

Condenser reproducers have heretofore been characterized by very feeble response to low pitch tones or sounds, such as arepro-y v duced by percussion instruments and French horns. and by an undesirable emphasls of high frequency sounds. The present invention provides a simple structure which sof-` tens or suppresses the unpleasant hlgh pitch reproduction, and brings out the full range of audible sound from the lowest bass up through the highest soprano with full rich overtones and brilliancy of reproduction.

v The embodiment as illustrated in Fig. 1, shows an expansible wood frame 1 which is frame 1.

1929. VYSerial No. 354,233.

used to support and stretch the condenser diaphragms 6, 8. Small wedges 2 may be driven into the corners of frame 1 for this purpose, causing all wrinkles to be drawn out taut. The condenser diaphragms 6, 8 should be kept taut, but not so tight that they resonate with a drum sound when struck by a persons hand. Instead, the sound on such test should be a dull thud. A row of tacks 4 serves to hold the diaphragms 6, 8 on the The size of frame 1 may be 16 inches by 24 inches, 20 inches by 30 inches,

.30 inches by 30 inches, or any other suitable intermediate area.

The acoustic condenser consists of a flexible elect-rode 7 permeable to air and acting as one ofthe two condenser diaphgrams, as shown in the diagram of Fig. 5, and a cooperating dielectric diaphragm 8 which carries a flexible metal coating or electrode 9. Numerous air passages 7 are rovided in flexible diaphragm electrode 6,. here is thus obtained a condenser of the order of mfd. capacity with both diaphragms 6 and 8 free to move in response to electrical strains applied thereto.

Referrin now to Fig. 2, a suitable embodiment` or the structure of flexible electrode 6 is shown. A woven metal fabric or tinsel cloth 10 is stretched over the frame 1. This cloth known in the trade as a metalline tinsel cloth consists of fine tinsel strands or ribbons running lengthwise, with textile cross threads holding same closely spaced apart. Either flat tinsel strands or crinkled strands may be used, but more efficient response is obtained from crinkled tinsel cloth, as shown in Fig. 3, probably because there is more working area in a given surface thereof.

The metal cloth 10 1s drawn free from wrinkles and suitably fastened to the frame 1 by tacks. Soft metal narrow strips or ribbons 12, such as lead or tin foil .02 inch thick ribbons are now pasted on the top of tinsel fabric 10. The distance between adjacent ribbons 12 may7 vary from 1 inch up to 8 inches, as the engthwise strips 12 serve as vibration dampening ribs for the metal cloth 10. Similar soft metal ribbons 11 are run crosswise across the metal cloth 10. Mucilage is suitable for fastening the strips 11 and 12, as same is conductive to electricity. If desired, a conducting powder may be mixed With the mucilage for this purpose, though some brands on the market are sufficiently conductive for the purpose when used `without such powder. The strips 11, 12 are smoothed down and adhere to the cloth 10. The crosswise strips 11 should be kmore closely spaced as they not only serve to dampen or control the vibrations of cloth 10, but also to electrically interconnect all of the individua-l tinsel strands thereof. vThe strips 11 may be 1/1 inch Wide, while the strips 12 are '3/8 wide. 1

A suitable spacing for strips 11 is from 1 inch up to 3 inches, according tothe size of frame 1. The flexible electrode 6 of Fig. 2 has the desired characteristics. It is light and flexible and freely permeable kto the passage of air. A multiplicity of'air passages is afforded by the spaces between the tinsel strandsV of metal cloth 10. The strips 11, 12 reinforce the cloth 10, and interconnect the ktinsel strands to make a unit electrode of large working area and sufficient combined area to serve as a sound diaphragm responsive to high frequencies and overtone components present in the exciting source used therefor. The lead strips 11, 12 are dull and soft, and impart no artificial resonance tothe diaphragm electrode 6. Moreover, the conductive strips 11, 12 afford sufficient inertia weight tothe cloth 10, to which same are attached, to carry low pitched sound without interfering with the air passages 13 provided therebetween, and

only partially covered by the tinsel cloth 10 with its numerous air passages 7 The crinkled tinsel cloth 10 has the desirable property also of stretching in both directions, lengthwise, as well as crosswise, when diaphragm 6 is in operation under the action of exciting sound producing source connected thereto. Electrode diaphragm 6 is thus light and thin and flexible. It is normally held substantially in a flat plane by frame 1, but may be moved both ways with respect thereto.

Referring now to Fig. 4, a suitable construction for the dielectric diaphragm 8, and its co-operating electrode or metal coating 9 is shown. Dmphragm 8 is 'composed of an impregnated fabric, such as empire cloth or a varnished silk or linen and may be .005 inch thick, though a thickness of .003 inch is suitable in the case of impregnated silk, and .010 Vin the case of cotton fabric.

I have found varnished cambric known as empirecloth, .005 inch'thick suitable forv diaphragm sheet 8. In use, it is stretched on top of the electrode diaphragm 6 on framel, as shown in Fig. 6 and heldto frame 1 by tacks. An insulating varnish size known as japan gold size, 18, is sprayed or lightly brushed over the top surface of dielectric sheet 8. By gold size japan varnish is meant such varnish as a definition of japan see t e new Standard Dictionary. Any japan will serve for/this purpose which hasV the necessar strength, dielectric strength, flexibilit a hesivenes's, etc. While varnish 18 is sti l wet, layers of thin metal foil, 15, 16 are rolled over varnished surface 18 of dielectric sheet-8 overs lapped, as shown at 14 to form strengthening overlap and electrical connection between strips 15, 16, etc. Any light foil is suitable for strips 15, 16, such as aluminum .00025 inch thick or lead tinfoil .0002 inch thick.

A narrow strip of lead foil 17 may be placed over the overlap rib 14, if desired, to assist the vibrationcont-rol afforded thereby. vDielectric diaphragm 8 is thus a good insulator. It is flexible, light, and has desirable dielectric constant for the purpose. The gold size varnish 18'tends to fill in any defects in the insulating cloth 8, as shown by 19 in Fig. 7,

and does not crack upon drying. The electrode 9 Vthereby afforded on dielectric 8 isV dielectric sheet 8 uncoated by metal foil elec` trode 9, as ,the corners at which insulating cloth 8 is stretched on frame 1 may be weakened during the stretching. While varnish 18 is still Wet, I prefer to apply a potential of about 600 volts to electrode 9 and electrode 6, Fig.r6, so tha-t'met'al foil strips 15, 16, etc. are drawn-tightly against varnished surface 18 of dielectric sheet 8 by electrical attraction. Electrode 9 carried by'dielectric sheet 8 is thus made firmly adherent and flexible, but not permeable to air flow therethrough.

The elements 8 and 9 of Fig. 4 thus acts as a single diaphragm ycapable of full response to the range of audible frequencies together with accompanying overtones without adding diaphragm resonance thereto. In

use, diaphragm 8 is stretched over electrode diaphragm 6, as shown in Figure 6, taut double diaphragms 3 are simultaneously i stretched to, bring flexible electrode 6, Fig.

therefrom by a very thin air layer 21. A

ridge portion 20 on frame l'insures this afore .6, close to the diaphragm 8, but separated 5 said action, leavingdiaphragm 8 free to move and electrode 6 free to move when electrical potential is applied to electrode 9 and to 'electrode 6. Sound waves are thereby set up by both diaphragms 8 and 6.

Connection can be made to metal foil 9 l by tinsel ribbon 22 pasted thereon" by mucilage, and to tinsel cloth 10 by flexible metal ribbon 23 held thereagainst by a tack 4. The

flexible screen electrode 6 vibrates as we1l as diaphragm 8 due to the aforesaid structure. The structure of this-flexible electrode lso 6 i`s further shown in Figs. 8 and 9, in which a coarser woven cloth or metallized cloth 10 is substituted in lieu of the tinsel cloth 10 of Fig: 2. The coarse cloth 10a may be metallized in any Vsuitable manner known in the arts, such as by the methods used in galvano-plasty, or by a metal spray coat applied thereto.

A suitable circuit for operating the acoustic condenser 3 is shown in Fig. 10. The amplifier tube has an input 24 from a radio set or phonograph electrical pickup device, and receives suitable energizing power from power unit 26. Output transformer 27 feeds audio potential to the acoustic condenser 3. A polarizer power unit 28 supplies about 400 volts direct current to series condenser 30 of 1 mfd. capacity. Acoustic condenser 3 reproduces the input supplied to input terminals 24 faithfully when power` units 26 and 28 are energized through conneet-or plugs 29 from a source of electric current.

Frame 1 may be suitably mounted or concealed in any suitable manner. Two or more condenser reproducers 3 may be connected in parallel operation, if desired. The acoustic condenser Bethus embodies the improved combinations and structures according to this invention by way of exemplification, and is characterized by the fact that it affords good volume and clear response according to the input fed to input terminals 24 of vacuum tube amplifier 25, Fig. 10. Diaphragms 3 are normally at rest in a substantially flat plane supported by frame 1. Strips 11, 12 serve as vibration dampening or vibration controllers for electrode 6. Varnish size 18 remains in flexible condition during use of the condenser 3.

4Vhile I have shown and described but a few embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made which do not depart from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. As an acoustic condenser reproducer, the combination of two flexible electrodes of dissimilar conducting area and a flexible dielectric sheet of impregnated fabric therebetween whereby both electrodes move under Variations in the electrical impulses to produce sound waves in the air.

2. An acoustic condenser comprising two flexible electrodes of dissimilar conducting area, one of said electrodes having metal strips woven therein and being permeable to air, anda flexible dielectric diaphragm, the other of said electrodes being fastened to said diaphragm.

3. An 'acoustic condenser comprising a flexible dielectric diaphragm composed of.

impregnated insulating cloth, a conducting electrode carried by said diaphragm, and a co-operating electrode placed adjacent to said diaphragm.

4. In an acoustic condenser the combination of a fabric impregnated with an insulating material, a flexible electrode carried thereon, and a second flexible electrode which is permeable to air flow stretched closely adjacent to said impregnated fabric, whereby the latter permeable flexible electrode is free to vibrate with respect to said impregnated'- fabric. f

5. An acoustic condenser consisting of a impregnated dielectric fabric, a flexible electrode carried thereon, and a co-operating flexible electrode including woven metal permeable to air flow stretched closely adjacent to said dielectric fabric whereby both electrodes move under Variations in the electrical impulses to produce sound waves in the air.

6. An acoustic condenser comprising a frame, a fabric stretched thereon, a tinsel cloth electrode supported loosely on said fabric and fastened to said frame, a dielectric sheet placed loosely over said tinsel cloth electrode and supported by said frame, a flexible electrode carried by said dielectric sheet, and means to stretch said frame to draw said tinsel cloth electrode closely adjacent to and separated by a very thin air layer from said dielectric sheet.

7. An acoustic condenser comprisingy a frame, a tinsel fabric electrode supported thereon, a dielectric sheet carried by said frame adjacent to said tinsel fabric electrode, a flexible electrode carried by said dielectric sheet, and means to expand said frame to 4draw said tinsel fabric electrode closely adjacent to and separated by a very thin air layer from said dielectric sheet.

8. In an acoustic condenser, a dielectric diaphragm comprising a woven fabric impregnated with an insulating compound, and an adjustable frame therefor to stretch same substantially in a flat plane.

9. In an acoustic condenser reproducer, a dielectric diaphragm comprising an oxidized insulatingoil impregnated cloth coated with gold size japan varnish.

10. In an acoustic condenser reproducer, a dielectric diaphragm comprising a fabric impregnated with an insulating oil and coated with a japan varnish size.

11. In an acoustic condenser reproducer, a dielectric diaphragm comprising an impregnated insulating cloth, a varnish coating on one surface thereof, and a flexible metallic coating carried by said varnish.

12. In an acoustic condenser reproducer, a dielectric diaphragm comprising an impregnated insulating cloth less than .O10 inch thick, a varnish size on one surface thereof,

endl a metallic coating carried by said var- 13. In an acoustic condenser reproducer, a dielectric diaphragm comprising an im- 5 preginated fabric approximately .005l inch thic a varnish size coating thereon and a metallic coating carried on said varmsh size coatin 14. condenser reproducer comprising flexible electrodes, and a co-o erating dielectric diaphra m therefor, sai dielectric diaphragm having a coating of flexible varnish size adhering to one of said electrodes.

15. In an acoustic condenser having electrodes, and a co-operating diaphragm therefor, the im rovement which comprises a plurality of vibration dam ening strips of soft metal attached to one oi) said electrodes.

16. In an acoustic condenser having eleczd trodes, and a co-operating dielectric diaphragm therefor, means to control the vibrations thereof comprising a plurality of soft metal strips fastened to one of said electrodes.

17. In an acoustic condenser having two flexible electrodes, and a co-operating diaphragm therefor, an expandible frame to stretch said diaphragm with respect to one of said electrodes to leave a very thin air $0 space therebetween.

, 18. An acoustic condenser comprising two flexible electrodes and a co-operating diaphragm therefor, one of said electrodes being carried by said diaphragm and an expandible frame adapted to stretch said diaphragm substantially parallel to the other of said electrodes.

19. An4 acoustic condenser comprising flexible electrodes and a dielectric diaphragm therefor, and means to stretch same substantially fiat and adjacent to each other, whereby a substantially non-directional acoustical reproduction may be had therefrom.

20. An acoustic condenser comprising electrodes, one of which is movable with respect to `the other, anda dielectric diaphragm` therebetween, said diaphragm comprising an oxidized insulating oil im regnated cloth.

In testimony whereof, have hereunto set my hand this 6th day of April, 1929.

PHILIP E. EDELMAN. 

